Noiseless single sample cycles renders
Cycles still is a approximation based path tracer. this means everything you see in the rendering is getting calculated by randomly shooting rays. per path blender is only shooting one ray per pixel (correct me if im wrong). this information contains "is this pixel getting light, or not". If yes, the pixel gets white, if not, it is getting black. this is why you only have black and white pixel at 1 rendered sample. If you shoot another ray, your information (light, yes/no) is getting mixed, so that a grayscale is calculated. the more sample pathes, the more accurate your image.

10 Samples is a good amount of samples and there is little you can do to even improve this number.

Only thing you can try is the upcoming denoiser for blender (download a WIP build here http://blenderartists.org/forum/showthread.php?395313-Experimental-2-77-Cycles-Denoising-build). But i dont think you can go under 5 samples.